(a) Field of the Invention
This invention relates generally to medical apparatus, and more particularly to a specific construction of an internal needle as a component of an indwelling intravenous needle.
(b) Description of Related Art
In the following, the construction of a commonly used indwelling intravenous needle will be described, referring to FIG. 2, an enlarged side view of such a needle. Reference numeral 1 refers to a tip of a cutting edge of a hollow internal needle 3, made of a metal, of an indwelling intravenous needle; the tip being beveled to make it easy for the needle 3 to pierce into the blood vessel. Numeral 4.sub.1 refers to an internal-needle base, made of a hard synthetic resin, of the internal needle 3; the inside thereof being formed wide so that the blood flowing backward from the inner bore 5 of the internal needle 3 can be collected.
Numeral 2 refers to a hollow external needle, made of a resilient translucent synthetic resin, covering the internal needle 3 in the vicinity of the rear of the beveled cutting edge 1 of the internal needle 3. The rear end of the external needle 2 is opened so that the tip of the internal needle base 4.sub.1 can be inserted, and that the blood or medicine passing through the inner bore of the external needle 2 is allowed to flow after removal of the internal needle 3 by connecting to a duct (not shown). An external-needle base 4.sub.2 is made of a synthetic resin of the same type as that of the internal-needle base 4.sub.1.
Now, description will be made on how to use the indwelling intravenous needle of the conventional type having the aforementioned construction. The indwelling intravenous needle in the state shown in FIG. 2 is pierced into the vein. As the internal needle 3 is pierced, and the blood is visually observed flowing backward in the inner bore 5 to point P on the internal-needle base 4.sub.1 ' the external needle 2 is left pierced in the vein. When the needle of the shape shown in FIG. 2 is pierced in the blood vessel, however, various problems are encountered, as shown in FIGS. 5(a)-(e). FIG. 5(a)-(e) is a schematic side view of assistance in explaining various problems encountered when the indwelling intravenous needle of the conventional type is pierced into the blood vessel. The indwelling intravenous needle is held in hand and pierced into the skin 9, advanced to a certain length, then the tip 1 is directed toward the vein wall 10, and further advanced until the cutting edge is felt reaching the vein cavity 11. At this point of time, the internal needle base 4.sub.1 is checked to see the state of the blood flow. If it is visually confirmed that no blood is flowing backward at point P (see FIG. 2) of the internal-needle base 4.sub.1 it means that the indwelling intravenous needle just comes in contact with the vein, or it has gone in a different direction from the vein. In the former case, the needle should be advanced more deeply, and in the latter case, the procedure must be repeated from the subcutaneous position. This state is shown in FIG. 5(a).
Next, if the blood is found flowing backward at point P of the internal-needle base 4.sub.1 it means the direction of the needle is correct, so the indwelling intravenous needle is penetrated further until the tip of the external needle 2 is felt reaching the vein cavity 11, then the internal needle 3 is extracted. At this point in time, if the blood is not found flowing backward to the external needle 2, it means that only the cutting edge of the internal needle 3 has reached the vein cavity 11 due to insufficient penetration. This state is shown in FIG. 5(b). In this state, if another attempt is made to cause the internal needle 3 to pierce again by replacing the internal needle 3 into the external needle 2, the attempt would fail. This is due to the swelling of an area around the vein, caused by the hypodermic bleeding flowing through the hole previously cut by the internal needle 3.
To avoid the state shown in FIG. 5(b) noted above, the entire indwelling intravenous needle is further advanced by the length of the cutting edge after the blood is found flowing backward at point P of the internal-needle base 4.sub.1. If the blood continues to flow backward at point P of the internal-needle base 4.sub.1 there is a likelihood that the external needle 2 can be smoothly advanced in the vein after the internal needle 3 is extracted. This is an ideal treatment. This state is shown in FIG. 5(c).
The blood, however, may flow backward at point P of the internal-needle base 4.sub.1 even in the state shown in FIG. 5(d) where the cutting-edge tip is pierced through the lower vein wall 10, with only the root 6 thereof left in the vein cavity 11. In this state, even when the blood back-flow in the external needle 2 is visually confirmed after the internal needle 3 has been extracted, any attempt to advance the external needle 2 could result in the external needle 2 hitting against the lower vein wall 10. Since areas around the vein wall 10 are swollen by the hypodermic bleeding flowing through the hole previously pierced by the internal needle 3, it is difficult to advance the external needle 2 into the vein cavity 11. In short, this could also lead to a failure.
Furthermore, if the blood back-flow at point P of the internal-needle base 4.sub.1 is discontinued halfway, it means that the entire internal needle cutting edge goes all the way through the vein, entering into one wall and leaving out of the opposite wall of the vein. This state is shown in FIG. 5(e). In this state, as the internal needle 3 is removed, and the external needle 2 is retracted until the tip thereof is returned in the vein cavity 11, the blood is then found flowing backward again. If the external needle 2 is advanced again at this point of time, the treatment may happen to succeed, but in most cases, would fail as in the case of FIG. 5(d), as described above. Thus, another attempt to pierce into the vein will be needed at a different location on the skin.
As described above, referring to FIGS. 5(a) through 5(e), the indwelling intravenous needle of the conventional type tends to be associated with frequent failures because of various problems in vein piercing operation. The success in vein piercing largely depends on the skill and intuition of medical men performing vein piercing. The main reasons for this can be summarized as follows.
One reason is that there is a time lag in confirming the start of blood backflow at point P of the internal needle base 4.sub.1 after the cutting-edge tip 1 of the internal needle 3 has been pierced into the vein cavity 11 because the internal needle is made of a translucent metal.
The second reason is that even if only the cutting-edge tip 1 and the cutting edge root 6 remain in the vein cavity 11, blood backflow at point P of the internal-needle base 4.sub.1 is continued. In other words, since the indwelling intravenous needle of the conventional type relies solely on blood back-flow at point P for estimating the location of the cutting edge 1 of the internal needle 3 in the vein, despite the above-mentioned two structural defects, it is considerably uncertain to grasp the relative positions of the cutting edge and the vein cavity 11. In short, blood back-flow from the internal needle 3 does not necessarily pinpoint the exact location of the tip of the external needle 2. This makes it difficult to quickly pierce the external needle 2 into a proper location in the vein cavity.